1. Field of the Invention
The present invention relates to an optical deflecting device that changes the direction of output light with respect to incident light and a method of manufacturing such an optical deflecting device, and also relates a technology suitable for image forming apparatuses, such as electrophotographic printers and copiers, and projection-type image and vide display apparatuses, such as projectors and digital theater systems.
2. Description of the Related Art
L. J. Hornbeck has disclosed digital micromirror device with a torsion beam hinge in Proceedings, The International Society for Optical Engineering (SPIE), vol. 1150, pp. 86-102 (1989). This technology has been expanded as disclosed in Proceedings of The Institute of Electrical and Electronics Engineers (IEEE), vol. 86, No. 8, pp. 1687-1704 (1998) by P .F. Van Kessl and J. Hornbeck, in which spatial light modulating device having a group of micromirrors is disclosed and called a Digital Micromirror Device (DMD) for use in image projecting device.
In these micromirror devices, mirrors are generally supported by a torsion beam called a hinge. By using the hinge, the reflection area is reduced. However, a DMD from Texas Instruments Incorporated has a two-storied structure provided with a reflecting member on the surface separately from the hinge portion. Also, with the use of the hinge, the actual voltage to be driven is as much as several tens of volts. However, for control on the order of 5 volts to 7.5 volts as data for switching the tilting direction, a bias voltage of several tens of volts to be applied all at one to a plurality of pixels and a restoring force of a special spring member are combined to switch the tilt.
Also, in a micromirror device reported in Micro Opto Electro Mechanical Systems-MOEMS '99 by Chang-Hyeon Ji and Yong Kweon Kim, a bearing-shaped hinge on a substrate without stiffness is used.
Furthermore, the inventors have submitted a patent application that discloses an optical deflecting device in which, with a displacement due to electrostatic attraction according to a potential applied to a member having a light reflecting area, a light beam incident to the light reflecting area is deflected with a reflecting direction being changed. The optical deflecting device includes a substrate, a plurality of regulating members, a pivot member, and a plate-shaped member. The regulating members each has a stopper on an upper portion and are provided to a plurality of ends. The pivot member has an apex formed of a conductive material and is provided on an upper surface of the substrate. The plate-shaped member does not have a fixed end, has the light reflecting area on an upper surface, and at least partially has a conductive material layer formed of a conductive member. At least a contact point making contact with the apex on a back surface is formed of a conductive member. The plate-shaped member is movably disposed within a space formed of the substrate, the pivot member, and the stopper, and provides a potential of the plate-shaped member through a contact with the pivot member (refer to Japanese Patent Application Laid-Open No. 2004-78136). Still further, the inventors have also submitted a patent application that discloses the invention having a bearing structure in which a plate-shaped member has formed thereon a notch and a protrusion (refer to Japanese Patent Application Laid-Open No. 2005-195798).
Other examples of the conventional technology include those disclosed in Japanese Patent Application Laid-Open No. 2004-138881, Japanese Patent No. 3492400, Japanese Patent No. 3411014, and Japanese National Phase PCT Laid-Open No 2002-525676.
In the spatial light modulator and optical deflecting device using a hinge, with the restoring force due to the stiffness of the hinge, the driving voltage is high, as much as several tens of volts. In high-definition and high-resolution television, for example, high-definition and high-resolution is required, and the number of pixels tend to be increased. When the number of pixels is increased, the chip size is expanded. In that case, a special process is required, and material cost is increased. Thus, the mirror dimension forming a pixel is required to be decreased. With this, the stiffness of the hinge hanging the mirror is increased, thereby increasing the driving voltage. For further downsizing, it is not easy to decrease the stiffness of the hinge because of limitations of microfabrication accuracy for making the hinge narrower. Moreover, if the stiffness of the hinge is tried to be weakened to decrease the driving voltage even for the purpose other than downsizing, the hinge is bent, and cannot sustain the center position of the mirror. Still further, when the hinge is used, the hinge is formed on the surface, and therefore the area that reflects light is decreased. To get around this problem, a complex structure has to be adopted in which a reflecting surface is formed on a driving electrode hanged by the hinge to form a double structure so as to increase the reflecting area. Still further, a post is formed to superpose the mirror on the electrode, but since the post has a hole, the mirror inevitably has an area where light cannot be reflected, thereby inviting a decrease in reflection efficiency. From these reason above, in the structure using a hinge, there is a problem in which downsizing results in a complex element structure and high manufacturing cost.
In the device reported by Chang-Hyeon Ji and Yong Kweon Kim, a simple bearing-shaped hinge is used. However, since the plated-shaped shaft moves within a rectangular frame, stability is low. Also, there are problems in which it is difficult to process a brace of the mirror and it is also difficult to downsize the mirror to a cube measuring 10 micrometers per side. Ensuring the accuracy of the bearing-shaped hinge is difficult. When mirrors are arranged in an array with high density to narrow a space between the mirrors, which may cause a loss of incident light, a problem of collision between adjacent mirrors occurs. Even in Japanese Patent Application Laid-Open No. 2005-195798, a constriction, a hole, and a protrusion are provided to the plate-shaped member, and therefore the light reflecting area of the plate-shaped member is sacrificed.